The role of cellular competition in B cell survival and selection of B cell repertoires

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Abstract
We studied the competitive repopulation by different B cells of irradiated mice reconstituted with bone marrow from either congenic or Ig‐transgenic (TG) mice mixed at different ratios. We found that after reconstitution, the number of B cells recovered in the different chimeras is similar and independent of the ratio of injected cells. In chimeras hosting TG and non‐TG cells, the relative representation of the donor cell lineages diverges from the ratios present in the inoculum, i.e. at the periphery, non‐TG cells are preferentially selected. Selection of non‐TG cells only occurs when population growth plateaus, i.e. when resources become limiting and competition starts to operate. Selection of non‐TG cells depends on surface Ig expression, and they are selected because they have a longer survival. Finally, the life‐expectancy of the same B cell population differs depending upon the second population present. The present results show that the life‐span and the population size of each B cell clone can be altered (interfered with) by the presence of a second cell population, demonstrating the existence of cellular competition among B cells. Our findings establish the role of cellular competition in the selection of B cell repertoires and the existence of a hierarchy of B cell selection in the absence of antigenic stimulation. The implications of cellular competition on our understanding of the immune system are discussed.